The present invention is directed to bonding particle materials, and more particularly to an apparatus for reactive or nonreactive synthesis, consolidation, or joining of metallic, ceramic, intermetallic, or composite materials to near-net shapes by application of high shear, high current (1-20 kA), and high pressure (about 1 to 2,000 MPa).
Pressure-assisted consolidation or sintering generally involves heating a particle powder compact, while applying pressure simultaneously. The powder compacts are typically heated externally using graphite or molybdenum heating elements and the pressure is applied hydraulically, pneumatically or isostatically using various types of gases depending on the type of the process. Conventional pressure assisted consolidation techniques include hot pressing, hot isostatic pressing, hot forging, and hot extrusion. The conventional techniques require long processing time and high chamber temperature in order to produce high-density parts. In addition, several preparatory steps are required, such as powder heat treatment, precompaction, canning, welding, and machining.
The field of powder consolidation includes powder particles with average particle sizes ranging from about 100 microns to less than 0.01 microns. In any powder consolidation process, the objective is to have minimum grain boundary contamination, maximum density and minimum grain growth. However, powder particles with large surface area, due to their surface charge distribution, readily react with the atmosphere and form a stable oxide phase, which significantly affects the consolidation process. The presence of these oxides, moisture and other contaminants on the surface of the particles, limits the final density that can be achieved and degrades the mechanical properties of the consolidated parts. Thus, it is important to reduce the surface impurities, such as oxygen and other contaminants present on the particle surfaces.
The consolidation of powders to near theoretical density, without significant grain growth has been a difficult task because of the tendency for the grains to coarsen at elevated temperature. Attempts have been made to consolidate powders with average particle size less than 0.01 microns by many techniques, such as furnace sintering, hot pressing, and hot isostatic pressing. However, the drawback is that the total time required for consolidation at the elevated temperature, is very long (several hours) which leads to significant grain growth, and poor mechanical and thermal properties.
Most refractory metals, ceramics, intermetallics and certain composite materials, are extremely hard and require diamond-tipped tools to machine them to final dimensions. In order to minimize expensive machining, the powder densification process must be capable of near-net shaping. The development of a novel equipment that consolidates the difficult-to-sinter materials into near-net shaped parts has been the goal of many powder metallurgy industries.
As application opportunities continue to emerge that require materials to perform at higher temperatures for sustained periods of time, joining of ceramic and intermetallic materials becomes necessary to enable advanced structure to be produced. Sinter bonding, sinter-HIP bonding, diffusion bonding are typically employed to join these advanced materials. However, long preparation and processing times are required in the conventional techniques that result in high manufacturing cost.
Metallic, ceramic, intermetallic, and composite materials have great potential in structural, electronic, thermal management and optical applications since these materials exhibit superior performance characteristics. Unfortunately, wide use of these materials is limited due to high cost of fabrication.
In summary, both the conventional (hot pressing, hot-isostatic pressing, sintering) and non-conventional powder densifying equipment (ROC-Rapid Unidirectional Compaction, Electroconsolidation, Quick-Hot Isostatic Pressing) are not designed for consolidating powders rapidly to full or near-theoretical density with minimum grain growth.
Various techniques and apparatus for compacting or sintering of powder materials are disclosed in U.S. Pat. Nos. 3,250,892; 3,340,052; 3,598,566; 3,670,137; 4,005,956; 5,084,088; 5,427,660; 5,529,746; and 5,794,113; and in publications--F. V. Lenel, "Resistance Sintering Under Pressure", Journal of Metal, Vol. 7, No. 1, pp 158-167 (1955), and M. J. Tracey et al., "Consolidation of Nanocrystalline Nb--Al Powders by Plasma Activated Sintering", NanoStructured Materials, Vol. 2, pp. 441-449 (1993).
The prior art apparatus are also not considered effective at least for the reasons that they: are limited to producing smaller size parts, result in nonuniform distribution of temperature throughout the powder compact, result in lower than near theoretical densities, result in undesirable grain growth, do not reactively consolidate or join the materials, do not consolidate or join precursor particle materials, require pretreatment or presynthesis of the particle material, do not apply to ultrafine particles (&lt;1 micron), etc.
In view of the above, there is a need in the industry for an apparatus that can rapidly consolidate, bond or join precursor or elemental particle material to near theoretical density without requiring complicated preparatory steps.